I agree, your comments on spontaneous inspiration are on-topic--and I never indicated they weren't; reread my comment.

As to my qualifications, not only do I speak from direct experience, but my advice agrees with that of professional coaches and creativity researchers--I've done my reading and test-driving. So, yes, I do consider my learning great, and my advice reflective of an informed concensus.

The fact is that the great majority of people (such as those who have to ask how) are not blessed with a spontaneously free-flowing font of musical ideas. To us, the most daunting, discouraging prospect is the silence, the blank page. To tell us "just wait for it, it'll come" is to offer useless and condescending advice--who passes up the right musical idea which occurs spontaneously? Our problem is that useful ideas largely don't occur without some form of provocation. For us, preparation and narrowing of focus are active, practical steps we can take to provoke "inspiration". It's a good way to open the floodgates to the level of flow we require, when we require. And it has been proven to work for most people who bother to apply it, not just for a lucky few.

Our brains excel in two things: pattern matching (analogous thinking) and targeted problem solving. Ideas come most readily when you can either liken your goal to something else or pose a question, the more specific, the better. That's really the core of the approach I've suggested. Basically: chunk down (narrow focus and reach a manageable level of granularity), consider similar things having the virtues you want, and ask guiding questions to give your problem a more well-defined form and provoke the creative responses you seek. Once you reach the right level or focus, ideas start to flow.